Cathode ray signal generator



June 23, 1942. c. E. BURNETT CATHODE RAY SIGNAL GENERATOR Filed Dec. l5,' 1 959 fi i .55.]

H ll l I V. \.!i iiii-iiiisi @SEEEEEQHEEIK M V M w Ym INVEN TOR. CARLOS E. BURNETT %fl%w ATTORNEY.

Patented June 23, 1942 CATHODE RAY SIGNAL GENERATOR Carlos E. Burnett, Maplewood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 15, 1939, Serial No. 309,396 '1 Claims. (01; 250-164 My invention relates to improvements in cathode ray signal generator tubes and particularly to an improved target electrode for use in such tubes.

In the usual form of cathode ray signal generator tube such as is used for developing signals representative of a single picture it is customary to scan with an electron beam a target having on its scanned surface a pattern or picture outline composed of a material having secondary electron emission characteristics different from those of the rest of the target. Thus, it has been customary to print or otherwise apply a pattern or picture upon a metal foundation using material such as a carbon ink having different secondary electron emitting properties than the metal. Suchtubes are difficult to manufacture because the baking and exhaust procedures produce variations in the secondary emitting property of the ink over different portions of the target;

It is an object of my invention to provide a cathode ray tube of the signal generating type wherein the pattern carried by the target and scanned by the electron beam has the desired beam and a target in the path of the beam provided with a picture or pattern of which a representation is to be transmitted, the said picture or pattern comprising materials having similar secondary electron emission properties and different physical properties. More specifically, I provide a target with a foundation having substantially uniform secondary electron emitting properties over its entire area and, in accordance with my invention, a pattern thereon made of at least two materials having different secondary emitting properties than the foundation, these materials having different physical properties, so that if one of the materials is rendered inefiective during manufacture of the tube, the otherjmaterial or materials perform their intended function.

These and other objects, features and advantages of my invention will appear from the following description taken in connection with the accompanying drawing in which:

Fig. 1' is 'a' cross-sectional view of a signal generating tube embodying my invention, and Fig. 2 is a plan view showing 'a target structure suitable for generating television signals and made in accordance with my invention.

In the illustrative embodiment of my invention shown in Fig. l the tube comprises a highly evacuated glass envelope or bulb I having a cylindrical neck section enclosing a conventional electron gun and a frusto-conical section enclosing a target 2 symmetrically positioned in the envelope so that its frontsurface may be scanned by a beam of electrons from the electron gun.

The electron gun assembly is of the conventional type, and comprises a cathode 3 from ably a conductive coating on a portion of the inner surface of the envelope I. The first anode 5 and the second anode 6 are maintained at the desired positive potentials with respect to the cathode 3 by a battery 1. Conventional deflection coils 8 and 9 or deflection plates may be used to sweepfthe beam in a horizontal and vertical plane, respectively, to scan the target 2.

As best shown in Fig. 2, the target 2 includes a foundation l0 which may be of metal or other material having relatively high secondary emitting properties. The foundation I0 is provided with a half-tone or line picture orpattern ll so that when the foundation bearing the pattern is scanned with an electron beam, signals are generated across the output impedance 12 which are suitable for transmission for the recreation of an image of the pattern, as is customary in television transmission and reception. The pattern I l is preferably applied to the. foundation by a printing process but 'it is obvious that it may be applied in any manner, such as by spraying through a stencil or' by engraving processes.

In accordance with my invention, the material used for making the pattern II is composed of a mixture of materials having similar secondary emitting properties, these properties differing from that of the foundation'lll. Preferably, the individual materials of which the pattern is composed have different physical properties so that any variation in the physical and electrical properties of one material during evacuation of the bulb I will not necessarily affect the electrical properties of the other material or materials.

Preferably, the material of which the pattern is made is a composite mixture of carbon and a metal oxide having secondary electron emitting properties similar to those of carbon. I have found that ferric oxide is particularly suited for this purpose because the process steps which may adversely affect the carbon will not affect the oxide, while at the same time, material containing carbon may be applied very easily and with great uniformity to the foundation and, in addition, the density of the pattern may be readily determined because of the. opjacity of the carbon in the material.

In the manufacture and assembly of the electrode shown in Fig. 2 I provide as the foundation ID a sheet of aluminum foil approximately .0O2-.005" in thickness and of the desired area. The sheet of aluminum is preferably provided with a backing sheet of cardboard or heavy paper which provides a good mat surface if the pattern II is to be applied by a printing process. The sheet of aluminum is then cleaned and the pattern having the desired outline is applied, such as by printing, using a printing vehicle or ink comprising in the most part carbon mixed with a small amount of ferric oxide. The amount of ferric oxide is not critical and the mixture may contain equal parts of carbon and ferric oxide by weight, although I havefound that a ferric oxide content of 5 to by weight gives excellent results, whereas the use of a greater amount of oxide renders the printing process more difficult.

The carbon is preferably carbon black or soot, although I have used finely divided graphite for this purpose with equal success. The carbon is mixed with the ferric oxide preferably in the proportion of 95 parts of carbon to 5 parts of ferric oxide by weight and with a binder to form a viscous paste. Since the carbon is mixed with the ferric oxide, the materials are commingled with each other making a homogeneous mass. The choice of a binder is not critical and binders such as usedin commercial printing inks may be used, although the binder should be volatile at temperatures below the temperature at which the tube is baked during the exhaust process.

The printing of the foundation Ill may be, done with a conventional half-tone or line out, and following the application of the pattern I I to the foundation ID the pattern is allowed to dry, whereupon the assembly may be fired to remove any volatile materials still present after drying. I have found that the firing step may be performed in an atmosphere of commercially pure hydrogen for a period of 5 minutes at 550 C. During this firing operation any oxidation of the carbon of the pattern due to traces of oxygen or water vapor in the hydrogen is immaterial because the presence of the ferric oxide maintains the electrical properties, such as the secondary emitting properties of the pattern, unchanged.

The foundation I0 is provided with a supporting frame [3 to which electrical contact may be made, and the electrode is sealed within the bulb I as shown in Fig. 1 with the surface of the foundation lil bearing the pattern H exposed to the electron gun so that the foundation and pattern may be scanned with the electron beam from the electron gun.

During the sealing in of the electrode Within the bulb, the carbon of the pattern may become oxidized, especially where the bulb is open to the atmosphere, as is usual practice in sealing in such electrodes. Such oxidation is, however, immaterial since the secondary electron emission properties of the carbon and ferric oxide are similar.

While I do not wish to be limited to any particular theory to explain the improved operation of my tube and electrode structure, I believe, as a result of a number of tests, that the presence of the ferric oxide protects the carbon from oxidizing and thus allows an even higher firing temperature to be used during either the baking of the electrode or during the sealing of the electrode within the bulb. Therefore, the presence of the ferric oxide protects the carbon from oxidization and the presence of the oxide maintains the secondary electron emitting properties of the pattern even if some oxidization of the carbon occurs during processing.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

I claim:

1. A cathode ray signal generator tubeincluding an electron gun for developing a beam of electrons and a target adapted tobe scanned by said beam, said target comprisinga foundation capable of liberating more than one secondary electron for each electron from said beamimpinging thereon and a composite coating over a portion of said foundation including a homogeneous mixture of at least two materials having similar secondary electron emitting properties and capable of liberating fewer secondary electrons than said foundation for each electron from said beam impingingthereon.

2. A cathode ray signal generatortube-including a target and an electron gun positioned to direct electrons to said target at sufficient'velocity to liberate secondary electrons from said target in excess of the electrons impinging thereon, and a composite coating on a portion of said target, said coating including aplurality of materials mixed together to form a homogeneous mixture, each of said materials having secondary electron emitting properties differing from those of said foundation by substantially the same amount.

3; A cathode ray tube including an" electron gun and an oppositely disposed target adapted to be scanned by a beam of electronsfromsaid gun, saidtarget including a metal foundation'having'a portion of its surface facing said gun covered with a composite coating including a homogeneous mixture of carbon; and ferricoxide.

4. A cathode ray tube as claimed in claim- 3 wherein the said foundation is aluminum andthe ferricoxide is at least 5% of said coating by weight.

5. A target for a cathode-ray tube including a metal foundation and a composite coating of carbon and ferric oxide mixedtogether'tofor-m-a homogeneous mass covering a-- portion of said foundation;

6. A target for a cathode ray tube comprising a sheet of aluminum and a composite homogeneous coating covering a portion of said foundation, said coating including carbon as its principal constituent and ferric oxide in a proportion of at least 5% ferric oxide by Weight with respect to said carbon.

'7. A cathode ray signal generator tube including a target and an electron gun positioned to direct electrons to said target to liberate secondary electrons in excess of the electrons impinging thereon, and a composite coating on a portion of said target, said coating being composed of a homogeneous mixture of carbon and a metal oxide capable of liberating fewer secondary electrons than those impinging thereon, said carbon and said oxide each having secondary electron emitting properties difiering from those of said foundation by substantially the same amount.

CARLOS E. BURNETT. 

